to see the real image we need a screen. yet i notice most simulation dun include a screen. I request that someone create an simulation that is something like the one in this thread but add a screen that is adjustable so we can see how does adjusting the screen affect the image. thx

I do not think the current version of EJS GUI can do the effect you need.But you can ask Paco to add it as part of EJS image property. Just provide him the source code and he should be able to implement it soon (if he think it is necessary).